This invention relates to filtering devices, and particularly to devices for filtering smoke and other combustion materials produced by burning waste products. Such materials are typically comprised of a gas component and a particulate component.
It is well known that the burning of certain waste materials gives rise to a large number of environmental pollutants including noxious gases and solid particulate matter. Not only are many of these by-products of combustion toxic and undesirable for emission into the general atmosphere, but many laws, at the Federal, State and local level, specifically prohibit the discharge of such materials into the air, waterways or other natural outlets. Therefore, it is essential that any polluting materials produced by combustion should be thoroughly and effectively treated so as to extract therefrom noxious gases and particulate matter so that they can be disposed of using environmentally sound and accepted methods.
Many devices and systems have been created to deal with the filtering of gas and particulate emissions depending upon their nature and source. Thus, many plants for the production of consumable products, chemicals and other materials may have associated therewith smoke stacks, the smoke stacks including various treatment and filtering devices for purifying the by-products of combustion prior to discharge into the water or atmosphere. Further, most vehicles, and many machines powered by the use of hydrocarbon fuels, are now fitted with mechanisms specifically designed for reducing the noxious by-products of such fuel combustion. For example, many automotive vehicles have fitted thereto catalytic converters, which contain a catalyst capable of converting potentially polluting exhaust gases into harmless or less harmful products.
There are many examples in the patent literature showing systems for filtering or cleansing combustion materials and particulate matter. U.S. Pat. No. 5,145,498 (Houston) is for a smoke stack exhaust system comprising a water-spray gas-scrubbing device. Waste gases from a building pass into a duct means and thereafter into a scrubbing chamber where they are mixed with water spray. The gas scrubbing water spray removes the particulate materials from the gases. The scrubbing water then passes through a filter tunnel, into a collector tray, through a filter tray and eventually the particulate material is removed from the scrubbing water.
U.S. Pat. No. 4,671,807 (Charlton) teaches a pollution control device for removing a wide variety of particulate matter and gaseous pollutants from the products of combustion. The system comprises a scrubber section, a charcoal filter section, and a dry filter section designed to remove both magnetic and particulate material. The scrubber section uses steam or water, while pipes in the filter section are filled with charcoal material.
U.S. Pat. No. 3,732,075 (Acaba) is for an air pollution control device including both mechanical and chemical filtering of the gases. First, a porous filter material precipitates and traps particulate matter, and, thereafter, a chemical filter reacts with the gases. The apparatus has a housing which includes the mechanical filtering means. Porous cloth-like and other filter material is used to trap various contaminants. The porous filter material may be made in the form of a bag to facilitate disposal of the collected dirt.
U.S. Pat. No. 5,480,619 (Johnson) teaches a combined regenerative scrubber and condensing heat exchanger system including a first heat exchanger for providing an initial cooling of flue gas and a second heat exchanger for further cooling. A spray reagent is introduced into the flue gas and onto the second heat exchanger for removing sulphur dioxide (SO.sub.2) from the flue gas and for cleaning the second heat exchanger. A regeneration device is provided to regenerate reagent from the reaction product.
U.S. Pat. No. 3,745,939 (Allbritton) describes effluent cleaner for trash burning and has three essential components, namely, a secondary furnace, a water pit and a stack. The secondary furnace receives a flow stream of effluent from a building, further combusts the materials, and passes the effluent to the water pit. In the water pit, the effluent is subjected to the action of spray nozzles, after which the effluent passes to the stack. Water spray nozzles are located in the stack for washing effluent as it flows upwardly from the water pit.
U.S. Pat. No. 3,299,620 (Hollingworth) discloses a gas treatment device comprising a recirculating pump which withdraws liquid from a reservoir and circulates it to spray chamber. A filter is provided and includes a low velocity simple dust, dirt and other common filter medium. There is also a filter which is of an electrostatic type, which supplements the action of the first filter. Thus, solids which may have passed through the first filter will hopefully be entrapped by the electrostatic type filter. A further absorbent-type filter is provided to remove certain compounds or gases. Above the chamber, there is an eliminator section for trapping moisture particles. Above the eliminator, another filter pack containing a series of filters is provided to remove pollutant gases, gaseous contaminants and the like.
U.S. Pat. No. 5,215,557 (Johnson) teaches a dry scrubber with integral particulate collection devices. The invention places a dry scrubber/particulate collection device in a single unit, and combines both operations. The invention shows a baghouse around the base of a chimney stack. Flue gas enters the baghouse where particulate material would be removed before proceeding to the stack. The removal of other contaminants, such as sulphur oxide, takes place at some other location before flue gas enters the baghouse. Johnson also describes a dry scrubber integrated with a particulate collection device. Hot flue gas enters the dry scrubber and is directed to a spray zone where mixing of the flue gas with sprayed droplets of an atomized alkaline solution takes place. In this way, sulphur oxide and other contaminants may be absorbed. The flue gas then passes through dampers to a particulate collection device, and thereafter through fabric filters of a baghouse.
Other patents/patent applications showing different forms of filtering systems include: U.S. Pat. Nos. 5,286,518; 5,512,257; 5,370,720; 4,208,381; and International Application No. PCT/SE88/00689.
Unlike any of the various filtering systems shown in the prior art, the present invention is for a two-stage system whereby, for example, smoke produced by the combustion of waste materials is subjected to a two-stage treatment. In the first stage, the smoke effluent containing a gas component and a particulate matter component is cooled to condense at least some of the various gases contained therein, and the condensed moisture is removed for disposal. In the second stage, the material remaining after cooling is subjected to a rigorous physical filtering system where dry particulate matter is extracted.